beginnings of untested mgrs implementation (chat gpt so probably wron…

…g ;-) )

src/commonMain/kotlin/com/jillesvangurp/geo/mgrs.kt

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+package com.jillesvangurp.geo
+
+import kotlin.math.roundToInt
+
+
+private val eastingLetters = "ABCDEFGHJKLMNPQRSTUVWXYZ" // Excludes I and O
+private val northingLetters = "ABCDEFGHJKLMNPQRSTUV"    // Excludes I and O
+
+data class MgrsCoordinate(
+    val longitudeZone: Int,
+    val latitudeZoneLetter: Char,
+    val eastingLetter: Char,
+    val northingLetter: Char,
+    val easting: Int,
+    val northing: Int
+) {
+    override fun toString(): String {
+        return "$longitudeZone$latitudeZoneLetter $eastingLetter$northingLetter $easting $northing"
+    }
+}
+
+fun UtmCoordinate.convertUTMToMGRS(): MgrsCoordinate {
+    val eastingLetter = getEastingLetter(longitudeZone, easting.toInt())
+    val northingLetter = getNorthingLetter(northing.toInt(), latitudeZoneLetter)
+
+    val eastingValue = (easting % 100000).roundToInt()
+    val northingValue = (northing % 100000).roundToInt()
+
+    return MgrsCoordinate(
+        longitudeZone,
+        latitudeZoneLetter,
+        eastingLetter,
+        northingLetter,
+        eastingValue.toString().padStart(5, '0').toInt(),
+        northingValue.toString().padStart(5, '0').toInt()
+    )
+}
+
+private fun getEastingLetter(zoneNumber: Int, easting: Int): Char {
+    val gridEasting = (easting / 100000)
+    val index = (gridEasting - 1 + (zoneNumber - 1) * 8) % eastingLetters.length
+    return eastingLetters[index]
+}
+
+//private fun getNorthingLetter(zoneNumber: Int, northing: Int): Char {
+//    val gridNorthing = (northing / 100000)
+//    val index = (gridNorthing - 1 + (zoneNumber - 1) * 2) % northingLetters.length
+//    return northingLetters[index]
+//}
+
+private fun getNorthingLetter(northing: Int, latitudeZoneLetter: Char): Char {
+    // Northing value should be adjusted for the false northing if in the southern hemisphere.
+    val adjustedNorthing = if (latitudeZoneLetter < 'N') northing + 10000000 else northing
+    // The northingLetters string starts with 'A' for 0m N, so no need to subtract 1 from the index.
+    val index = (adjustedNorthing / 100000) % northingLetters.length
+    return northingLetters[index]
+}
+
+
+fun convertMGRSToUTM(
+    zoneNumber: Int,
+    zoneLetter: Char,
+    gridSquare: String,
+    easting: Int,
+    northing: Int
+): UtmCoordinate {
+    val eastingLetter = gridSquare[0]
+    val northingLetter = gridSquare[1]
+
+    val eastingOffset = getEastingOffset(eastingLetter, zoneNumber)
+    val northingOffset = getNorthingOffset(northingLetter, zoneNumber, zoneLetter)
+
+    val fullEasting = eastingOffset * 100000 + easting
+    val fullNorthing = northingOffset * 100000 + northing
+
+    return UtmCoordinate(zoneNumber, zoneLetter, fullEasting.toDouble(), fullNorthing.toDouble())
+}
+
+private fun getEastingOffset(eastingLetter: Char, zoneNumber: Int): Int {
+    val eastingIndex = eastingLetters.indexOf(eastingLetter)
+    return (eastingIndex + 1 - (zoneNumber - 1) * 8 + eastingLetters.length) % eastingLetters.length
+}
+
+private fun getNorthingOffset(northingLetter: Char, zoneNumber: Int, zoneLetter: Char): Int {
+    var northingIndex = northingLetters.indexOf(northingLetter)
+    northingIndex = (northingIndex + 1 - (zoneNumber - 1) * 2 + northingLetters.length) % northingLetters.length
+
+    // Adjust for the latitude band
+    val northingBase = "CDEFGHJKLMNPQRSTUVWX".indexOf(zoneLetter.uppercaseChar()) * 8
+    return (northingBase + northingIndex) % northingLetters.length
+}
+
+
+

src/commonTest/kotlin/com/jillesvangurp/geogeometry/MGRSTest.kt

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+package com.jillesvangurp.geogeometry
+
+import com.jillesvangurp.geo.convertUTMToMGRS
+import com.jillesvangurp.geo.toUtmCoordinate
+import kotlin.test.Test
+
+class MGRSTest {
+    @Test
+    fun shouldCalculateMgrsForBrandenburgerTor() {
+        val mgrs = brandenBurgerGate.toUtmCoordinate().convertUTMToMGRS()
+        println(mgrs)
+    }
+}